It is common for the manufacturers of electrical equipment to test such equipment before packaging and shipping the equipment to distributors, sales outlets, end users and the like. Such testing may include checking the various modes of operation of the equipment for satisfactory performance, proper adjustment of controls within prescribed tolerances, operating ranges, etc. and it may also include several hours or days of operation ("burn-in") to check for stability and to detect possible premature failure. Still other tests may involve running the equipment under specified overload conditions, performing tests of certain components or portions of individual circuits within the equipment, and checking for weaknesses or the presence of defective components or other circuit parts which may not be readily apparent from test operation of the equipment. It is not uncommon for others down-line in the distribution channel leading to the ultimate end user to perform similar tests of the equipment before final disposition.
A cardiac pacemaker is a type of electrical equipment in which testing for proper, reliable operation is essential. Because of the nature of the use of a pacemaker, it is literally true that a life may be at stake if a pacemaker malfunctions during operation when implanted in a patient. For this reason, elaborate tests are performed during the manufacture of pacemakers to make them as reliable as possible.
A further, relatively unique demand is imposed on pacemakers by virtue of their ultimate use. The pacemaker and all of its internal components must be surgically sterile. Thus, after manufacture and testing, the pacemaker is sterilized and sealed in sterile packaging, to be maintained in sterile condition until the packaging is removed in preparation for implantation of the pacemaker by a surgical team.
An appreciation of the problem of testing an electronic component in a sterile package without invading the internal sterile environment of the component is evidenced in U.S. Pat. No. 4,605,007 of Heraly. That patent discloses an inner and outer container with feedthrough contacts in the outer container to physically contact the electrical contacts of the sterilized electrical component. Thus circuit connections may be established with the outer contacts without affecting the sterile condition and environment of the inner contacts that constitute part of the electrical component in the sterile environment. This component, however, is only a part of a cardiac pacemaker and is not subject to the problems of testing the terminal connectors and lead circuitry of an overal pacemaker. The provision of access to an internal, prepackaged electrical component which is taught by Heraly is akin to that which is customarily provided for testing drycells that are commonly marketed in a bubble pack package. A pair of small holes in the bubble pack are provided next to the drycell terminals so that a pair of voltmeter electrodes can be applied to the terminals without opening the package. Heraly adapts that principle to protection of a sterile environment in which an electrical component is packaged.
It is generally possible to conduct certain tests of pacemakers while they are still enclosed within their sterile packaging. Modern pacemakers not only can receive programmed instructions, but they can also send back messages regarding the status of the pacemaker. This ability to remotely interrogate the pacemaker by wireless means is called telemetry. Telemetry can provide a readout of the various programmable functions of a pacemaker and an indication of the properties of certain of the pacemaker components. Final testing of a cardiac pacemaker is generally performed by the surgical team in preparation for implantation. It is common to have a plurality of pacemakers at hand, still in their sterile packaging, in the operating room at the time of final testing so that no time need be wasted in drawing another unit from inventory if a defect is discovered in the one under test.
Heretofore it has been difficult, if not impossible, to provide a final test of the terminal connectors for the leads which are to be inserted in the patient's heart and plugged into the pacemaker for implantation, yet these terminal connectors constitute one of the important potential failure points of a pacemaker. While certain types of terminal failures may be detected at final telemetry testing, others cannot. For example, an unusually low impedance in the terminal connector circuit may suggest a break in insulation. However, since the terminal circuit is open prior to connection to the heart leads, a break in a wire leading to the terminal does not provide any different indication and therefore cannot be detected until the leads are connected to the pacemaker. Detection of such a failure at this points represents a setback in the surgery time schedule, necessitating the susbsitution of another pacemaker which requires duplication of the programming, testing. etc. already conducted on the first pacemaker.